You should get a doctor, you at least need something in your medical history to document that kind of stuff. I would think it might not be a bad idea to see one once in a while anyway. All you need to go legal is a doctors recommendation, but it might be hard to find a regular doctor that'll give you that, especially if its your first visit, but if you can do that you could avoid a pot doctor and their fee, (usually from $150-200).

You will need something in your medical history to give a reason for using marijuana, the pot doctor doesn't guarantee the recommendation, you could end up paying and not get it if you don't have the medical records. I don't know how common that is, many pot doctors are a bit shady, but I do think they need something in your medical history to write you a recommendation. If you were in so cal I'd give you the website of the place I went to, they were very helpful, but I don't think they have any offices in Northern Cali.

Good Luck!